This invention relates to a method of producing a bituminous foam. An apparatus for carrying out the method and a method using the foam are also described.
This invention relates to a method of producing a bituminous foam. An apparatus for carrying out the method and a method using the foam are also described.
Foamed bitumen binders have been known for many years. For example, up to and during the late 1940""s and 1950""s, when steam road sprayers and steam rollers were commonly used in road preparation, foaming of a coal tar binder was an established practice for use in grouting techniques and for stabilisation of road bases. In the process, superheated steam was used to raise the temperature of tar to about 120xc2x0 C. prior to injection of low pressure steam (wet steam) immediately prior to discharge through a hand lance or spray bar jets. This provided a crude (but nonetheless effective) means of creating foam thereby to increase the volume of the tar (binder) and assist dispersion of the tar into a road under construction immediately after contact of the tar with the road, roller tines and harrows were used to effect in situ mixing.
U.K. Patent No. GB 1 325 916 (Mobil) describes a method and apparatus for producing foamed materials, especially foamed bituminous materials. The method essentially comprises providing bitumen at an elevated temperature and then mixing the hot bitumen with a liquid, for example water, which is insoluble in the bitumen. The liquid evaporates on discharge of the mixture to ambient conditions and thereby causes expansion of the bitumen which, accordingly, foams. Thus, in essence, the method comprises a two-stage process. Disadvantageously, the two stage process necessitates very careful control of the flow rates of the bitumen and water and, accordingly, relatively complicated apparatus. Furthermore, the second stage of the process is potentially hazardous due to the violent reaction between hot bitumen and water.
It is an object of the present invention to address the above described problems.
According to a first aspect of the present invention, there is provided a method of producing a bituminous foam, the method comprising raising the temperature of an emulsion which includes bitumen and a liquid which is substantially insoluble in said bitumen (hereinafter xe2x80x9csaid insoluble liquidxe2x80x9d); and discharging said emulsion from a first environment wherein the pressure is P1 to a second environment wherein the pressure is P2 and P1 greater than P2, whereby said emulsion foams after discharge into said second environment.
Said insoluble liquid may be such as to produce a relatively high ratio of vapour per wt % thereof included in said emulsion. To this end, said insoluble liquid preferably has a low molecular weight which is suitably less than 100, preferably less than 80, more preferably less than 65. Said insoluble liquid may comprise a mixture of components. Said insoluble liquid may be water or a lower alcohol, especially a C1-3 alcohol, or a mixture comprising any of the aforesaid. Preferably, said insoluble liquid comprises a major amount of water.
In the context of this specification, a xe2x80x9cmajor amountxe2x80x9d may mean at least 60 wt %, suitably at least 75 wt %, preferably at least 90 wt %, more preferably at least 95 wt %, especially at least 99 wt % of the referenced component is present in a referenced formulation.
Preferably, said insoluble liquid consists essentially of water.
In the method, the temperature of said emulsion is suitably raised, under said pressure P1, to a temperature at which it can vaporize sufficient of said insoluble liquid to produce the amount of vapour required for the desired expansion of the bitumen on foaming after discharge into said second environment. The emulsion may be exparded to produce a foam in said second environment, wherein the ratio of the volume of foam to the volume of said emulsion present initially is at least 5, suitably at least 10, preferably at least 15, especially at least 20.
The temperature of said emulsion at discharge is preferably greater than the boiling point of said insoluble liquid, suitably by at least 100xc2x0 C., preferably at least 150xc2x0 C., more preferably at least 200xc2x0 C., especially at least 250xc2x0 C.
The temperature of said emulsion at discharge is suitably not more than 100xc2x0 C., preferably not more than 80xc2x0 C., more preferably not more than 60xc2x0 C., especially not more than 50xc2x0 C., greater than the boiling point of said insoluble liquid.
The temperature of said emulsion at discharge may be at least 105xc2x0 C., suitably at least 110xc2x0 C., preferably at least 115xc2x0 C., more preferably at least 120xc2x0 C., especially at least 125xc2x0 C.
The temperature of said emulsion at discharge may be less than 200xc2x0 C., suitably less than 190xc2x0 C., preferably less than 180xc2x0 C., more preferably less than 170xc2x0 C., especially less than 160xc2x0 C.
In the method, the temperature of the emulsion may be raised through at least 20xc2x0 C., suitably at least 40xc2x0 C., preferably at least 60xc2x0 C., more preferably at least 80xc2x0 C., especially at least 100xc2x0 C. The temperature may be raised through less than 200xc2x0 C., suitably less than 180xc2x0 C., preferably less than 160xc2x0 C., especially through less than 140xc2x0 C.
The temperature of said emulsion immediately prior to it being raised in the method may be at least ambient temperature.
Said emulsion preferably has a viscosity at 20xc2x0 C. in the range 0.2 to 800 Poise. The viscosity at 80xc2x0 C. may be in the range 0.1 to 100 Poise
A first heating means is suitably provided for raising the temperature of said emulsion. Said first heating means preferably does not cause a change in concentration of said bitumen or said insoluble liquid in said emulsion as would occur, for example, if a heated liquid was contacted with said emulsion for heating it. Said first heating means preferably comprises a heated solid body arranged to transfer heat to said emulsion by conduction. For example, said emulsion may be passed through a convoluted heating assembly, for example a heating coil, which may be heated by suitable means, for example by circulation of a heated fluid and/or by electrical heating means.
Preferably, in the method, said temperature of said emulsion is raised as described herein when said emulsion is in said first environment. Thus, said temperature is preferably raised whilst said emulsion is within an apparatus in which the pressure is P1.
Preferably, P1 is at least 1.0xc3x97105 N/m2, more preferably at least 1.5xc3x97105 N/m2, especially at least 2.0xc3x97105 N/m2. P1 may be less than 4xc3x97105 N/m2, preferably less than 3.5xc3x97105 N/m2, more preferably 3.0xc3x97105 N/m2 or less.
Preferably, the pressure of said emulsion is raised to said pressure P1 in said first environment. Prior to entry into said first environment, the emulsion may be at a pressure of less than P1 which may be ambient pressure.
P2 is preferably ambient pressure.
The temperature in said second environment is preferably less than the temperature in said first environment, suitably by at least 50xc2x0 C., preferably at least 60xc2x0 C., more preferably at least 70xc2x0 C., especially at least 80xc2x0 C. The temperature in said second environment is preferably ambient temperature.
The method is suitably carried out in an apparatus having a first region in which the pressure of an emulsion therein is arranged to be raised to said pressure P1. An inlet is suitably provided for passage of an emulsion into the first region and an outlet is suitably provided for passage of the emulsion, under pressure, out of said first region, suitably to said second environment. Said first heating means described above is suitably provided between the inlet and outlet for heating the emulsion in the first region. A first pump means is suitably provided for pumping the emulsion within the first region and, suitably, for raising the pressure thereof. The apparatus may be arranged for circulating the emulsion within the first region. First outlet valve means is suitably provided for allowing the passage of said emulsion, under pressure, out of said first region from where it may be directed to a desired location.
A feedstock supply means is preferably provided upstream of said first region. In the method, said feedstock supply means suitably contains said emulsion prior to its supply to said first region wherein its temperature is raised. The emulsion associated with said feedstock supply means is preferably held at ambient pressure. Said emulsion may be held at ambient temperature. It may, however, be desirable for a second heater means to be associated with said feedstock supply means, wherein said second heater means is arranged to raise the temperature of the emulsion associated with said feedstock supply means. Said second heater means may be arranged to raise the temperature to at least 40xc2x0 C., suitably at least 50xc2x0 C., preferably at least 60xc2x0 C., more preferably at least 70xc2x0 C., especially to at least 80xc2x0 C.
Preferably, the only feedstock used in said method is a feedstock of said emulsion. That is, suitably no water, steam and/or other feedstock is separately fed into said apparatus.
Preferably, the composition of said emulsion in the feedstock supply means is substantially the same as the composition of the emulsion when present in said first region, after heating. That is, preferably, no component (especially no water or steam) is added to the emulsion after entry of it into said first region.
Said apparatus may include a second region in which the pressure of an emulsion therein is arranged to be raised to a pressure P1. An inlet for passage of emulsion into said second region may communicate with an outlet from said first region. Said first pump means described above is preferably arranged to pump emulsion in said second region. Means may be provided for raising the temperature of the emulsion in said second region. Second outlet valve means is suitably provided for allowing passage of said emulsion, under pressure, out of said second region from where it may be directed to a desired location.
Said emulsion used in said method may include at least 50 wt %, suitably at least 55 wt %, preferably at least 60 wt %, more preferably at least 65 wt % bitumen. Said emulsion may include 95 wt % or less, suitably 90 wt % or less, preferably 85 wt % or less, more preferably 80 wt % or less of bitumen.
Said emulsion suitably includes at least 10 wt %, preferably at least 15 wt %, more preferably at least 20 wt % water. Said emulsion may include 45 wt % or less, suitably 40 wt % or less, preferably 35 wt % or less, more preferably 30 wt % or less of water.
Said emulsion may have a pH of at least 1, preferably at least 1.5. The pH may be 5 or less, suitably 4.5 or less, preferably 4.0 or less, more preferably 3.5 or less.
Said emulsion may include an inorganic acid for adjusting the pH. Alternatively, an anionic emulsion may be prepared using a sodium hydroxide pH balanced aqueous phase so that the finished emulsion has a pH in the range about 11-12.
Said emulsion preferably includes one or more surface active agents, for example emulsifiers and/or adhesion agents. The total amount of surface active agents present in said emulsion may be at least 0.1 wt %, preferably at least 0.15 wt %, more preferably at least 0.20 wt %. The total amount may be less than 2 wt %, preferably less than 1.5 wt %, more preferably less than 1.0 wt %, especially less than 0.8 wt %.
Said emulsion may be anionic, cationic or non-ionic in nature and said surface active agents may be selected accordingly. Preferred surface active agents are amines, for example N-alkyl tallow 1,3-propylene diamine, derivatives of tallow propylene diamine and associations of alkylamido polyamines and alkyl imidazo polyamines, and lignosulphonates.
The surface active agents may be primarily for maintaining the water as an emulsion in said bitumen. However, the presence of suitable surface active agents may enhance the end performance of the foam by, for example, aiding stone coating and cohesion in low temperature techniques. Alkylamidoamines/polyethylene polyamine combinations and lignosulphonates may be particularly useful in this regard.
Said emulsion may include a modifying means for modifying the properties of the bitumen. Preferred modifying means may be organic polymers or copolymers, for example styrene-butadiene polymer, styrene-butadiene-styrene copolymer, ethylene vinyl acetate polymer, and oils, for example tall oils and/or any of the individual constituents thereof.
Where a modifying means is provided in said emulsion, it may contain less than 7 wt %, suitably less than 6 wt %, preferably less than 4 wt %, more preferably less than 3 wt %, especially 2 wt % or less of said modifying means.
Said emulsion may include flux oils (volatile or non-volatile), for example in the event that the foam is to be used as a means of reactivating residual bitumen in recycled road materials.
According to a second aspect of the invention, there is provided an apparatus for producing a bituminous foam, the apparatus having a first region for containing an emulsion wherein a first heating means is provided for raising the temperature of said emulsion and a pressure means is provided for raising the pressure of said emulsion to a pressure P1, an inlet being provided for passage of a feedstock from a feedstock supply means into said first region and an outlet being provided for passage of the emulsion out of the first region and into a second environment at a pressure P2, wherein the pressure P2 is less than P1.
Said feedstock supply means preferably contains an emulsion which includes bitumen and a said insoluble liquid. Said first region may contain an emulsion which includes bitumen and a said insoluble liquid.
According to a third aspect of the invention, there is provided a method of contacting a substrate with a bituminous foam, the method comprising directing foam produced according to said first aspect and/or using an apparatus according to said second aspect towards said substrate thereby to contact it.
Said substrate may be stone or a road (or other) surface. Said substrate may comprise particulate material.
The invention extends to a bituminous foam when produced in a method according to said first aspect and/or using an apparatus according to said second aspect.
Any feature of any aspect of any invention or embodiment described herein may be combined with any feature of any aspect of any other invention or embodiment described herein.